The invention relates to a metal-cutting tool, in particular a rotary tool and preferably a reaming tool, comprising a center axis and comprising a cutting part having a peripherally arranged cutter which, upon rotation about the center axis, defines a cutting circle of nominal diameter, and further comprising two peripherally arranged guide elements.
A metal-cutting tool of this type can be derived for example, in the form of a single-blade reamer, from DD 230810 A1 and from DE 39 39 339 A1.
Reamers of this type are used for the finishing of boreholes. In this context, highly accurate roundness and straightness, as well as a high surface quality of the inner wall of the bore, are of material importance. In the case of a plurality of simultaneously machined boreholes, a precise coaxiality of a plurality of boreholes is additionally of importance. A typical application is the inner surfaces of bearing components, for example in engines.
In order to obtain the best possible drilling results (roundness, straightness etc.), in reaming tools of this type, which often have only a single reaming cutter, guide elements, usually in the form of bars, are attached to the periphery of a tool main body. The radially outermost points of the guide elements lie at a same radial distance to the center axis and, upon an imaginary rotation about the center axis, define a guide circle. Correspondingly, the cutter, upon rotation about the center axis, defines a cutting circle. The diameter of the guide circle is here consistently smaller than the diameter of the cutting circle.
In the machining operation, the tool is deflected due to the generated metal-cutting forces until the guide elements come to bear against the inner wall of the bore. Due to this deflection, in the machining operation the center axis of the tool itself, in turn, runs on a circle, which circle should run concentrically to the desired borehole axis.
In order to ensure the necessary contact of the guide elements against the inner wall of the bore, the deflection force which is generated in the cutting operation must be sufficiently large to overcome the elastic restoring force of the tool. Particularly in tools having larger diameters and having a consequently high natural rigidity, in the machining of soft lightweight materials, such as, for example, aluminum or magnesium alloys, the problem arises, however, that insufficient deflection force is generated in the cutting operation. This can sometimes lead to a poor and undefined guidance of the tool, so that the desired dimensional precision, in particular a desired roundness, cannot be maintained within predefined tolerances.
A further problem exists in the machining of through holes. At the end of the borehole, the deflection force dramatically declines, whereby the entire tool leaps back into the center of the borehole. As a result, damage can occur to the produced borehole surface. This problem also exists in the withdrawal from the produced borehole, since the tool springs back and penetrates the already machined surface and damages the same.